Can anyone explain the difference between the Yagi antenna configurations between the 2.4 GHz and 5.8 GHz. Why does the 5.8 GHz have shorter bars and the 2.4 GHz longer bars? I kind of understand it's the frequency tuning but not entirely. Thanks in advance.
mavic mini yagi antenna (CE)
- Thread starter sunshinewelly
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Pushkur
Well-Known Member
GerdS
Well-Known Member
The bar length must match to a multiple of the wavelength. Please use Google or go to there: Wavelength - Wikipedia
Made some digging when I bought my Yagis ... & if I remembering correctly the bar length is 2 x frequency amplitude.
It does not have to be 2x. A wave follows a sine function. One full sinus period is called one wavelenght and in order to be able to 'escape' an antenna, the wave must 'fit' in the antenna. If it does not fit, some part of the wave will bounce back in the antenna in the form of energy hitting the transmitter. If too much energy is bounced back, the transmitter can get 'blown' up, in other words is destroyed. It is a bit technical to explain, but when the antenna is e.g. 1/2 of the wavelength, it will bounce back in such a way that it fits the outcoming wave and that is ok. But when it does not fit (e.g. when the antenna is 0.62 of a wavelenght) it generates interference waves with the waves that want to come out of the antenna and those will be trapped in the antenna. It will hit the last amplifier stage of the transmitter and that will burn it.
The relation between frequency and wavelength is simple: wavelenght = speed of light / frequency. So, for example if a radio station transmits at 100 MHz it will generate sine waves with a wavelenght of 300 000 000 m/s divided by 100 000 000 Hz = 3.0 meter. So the antenna will have to be 3,0 meter in ideal conditions or a multiple of it and that's why they call it the 3 meter band. The ratio between the incoming and outcoming wave (so the ratio in which they fit each other is called the SWR (standing wave ratio) and is ideally 1.0000000. The higher the SWR the more it is a misfit and that will get you into trouble. That is the reason why all radioamateurs have a SWR meter installed to keep an eye on the efficiency of the antenna and to prevent damage to the receiver.
A receiver has to have, in ideal conditions, also a multiple of that wavelenght in order to 'catch' the incoming wave with maximum efficiency.
That is why I wrote in #5 of this topic to be careful with extenders. If they don't match they can destroy your RC! The lower the frequency, the shorter the waves (as can be seen in the relation equation above). A frequency of 2.4 GHz corresponds to a wavelenght of 0.125 meter and 5 GHz to a wavelenght of 0.06 m so only 6 cm!). The shorter the wavelength the more accurate the antenna lenght has to be. If you transmit at 5 GHz with an antenna lenght of 0.05 m the SWR will be 0.06 / 0.05 = 1.2 so already 20% of the radiated energy will bounce back, generating heat in the last amplifier stage.
Greetings from Belgium!
Ronny (radioamateur ON4CAY, that is why I know a bit more of the technical details of antennas etc)
@Ronny St. thanks for explanation.
I just got news that my Yagi ordered from eBay has arrived, for 2.4 GHz and 5.8 GHz.
So as I understood they can be made in the wrong way. So if they work that means that they can't harm receiver?
I suppose the best way to test them is to fly without them and when signal start to break I put the extenders and if signal get stronger and I can fly a bit further, and repeat that test several times, then Yagi works.
I just got news that my Yagi ordered from eBay has arrived, for 2.4 GHz and 5.8 GHz.
So as I understood they can be made in the wrong way. So if they work that means that they can't harm receiver?
I suppose the best way to test them is to fly without them and when signal start to break I put the extenders and if signal get stronger and I can fly a bit further, and repeat that test several times, then Yagi works.
It is not only a matter of working or not. A completely mismatched antenna (as it is called) will work but with very low efficiency and finally will harm and destroy your transmitter see my explanation above). It is all a matter of time before the last amplifier stage of the transmitter will break down...
So please be very, very carefull with all modifications on the antenna part of your RC! As there is obviously no SWR meter built in, you don't have a clue if you are harming your RC before it finally will break down. That is the reason why I do have not the intention to experiment with antenne extenders unless I would know for 100% that they are made very accurate.
This require a bit more clarification ...
So by saying that you get a low efficiency but they work ... do you by that mean that the RC transmits but you actually see a worse performance regarding distance & live view breakup.
Or ... do you mean that even though the transmission range extends largely & the live feed gets rock solid, you can have low efficiency with risk of harming the transmitter?
You will have a lower transmission range due to the fact that not all energy is transmitted. So if there is an antenna mismatch you will see a decreasing range. If that is the case than you are harming your final amplification stage of the transmitter and it is just a matter of time before it will give up.
Well, them I'm safe with my Yagis ... see definitely an improvement both in distance, live feed stability & interference penetration ?
Do you experience improvement in both bands, in 2.4 GHz and in 5.8 GHz?
I live in city and auto always choose 5.8 GHz, few times when I checked all 2.4 GHz band bars are red and long, so probably I will not be able to manually choose 2.4 GHz. So no use for 2.4 GHz Yagi in the city. That's why I'm interested how good is 5.8 GHz Yago in the city, because I somewhere read that Yagi is good only for 2.4 GHz, and I really hope that is not the truth.
The other thing that concerns me is that with Yagi you must precisely point controller toward drone. I don't know yet how precise (moderately or insanely precise). With stock controller i like that I have some level of freedom where at least in close distance I can stand in any direction and it works.
Yes ... but don't know for sure how much better a Yagi is to penetrate a lot of interference, have tested to fly over a smaller industrial area which have a couple of taxi cab headquarters ... couldn't pass over there before, probably due to interference coming from them to make contact with their cars. With the Yagi I can pass over with only minor live feed hiccups. The few occasions when I fly in city centers I always stay really close.
But with or without Yagis the most destructive for the connection is going out of unobstructed LOS, get something in between RC & AC & the connection breaks up pretty fast.
Yes, that is true.
I wonder is OccuSync better in that matter also (not just for better distance).
You can only check that using an SWR meter between transmitter and antenna, but that is not possible with the built-in antennas of the MM. So the only way is to test them and see if your range increases.
Based on your detailed knowledge, what should be the exact lengths of each metal bar — and the distance between them — for both 2.4 and 5.8? Then people can check their yagis with a ruler or even a micrometer/caliper.
Well, you have to use the equation I've given above: wavelength (in meter) = speed of light (in meter per second)/ frequency (in Hz). The speed of light is 300 000 000 m/s.
So if your frequency is exact 2.4 GHz (thus 2400 000 000 Hz) that gives you 0,125 meter so 12,5 cm and for 5,8 GHz (so 5800 000 000 Hz) that yields 0,051724... meter or 5,1724 cm.
Thanks. For practical reasons, those lengths may be too cumbersome, so could an exact fraction be used instead, e.g. ½ so 6.25 cm and 2.5862 cm respectively? It appears that’s what the yagi antennas you can buy online have done. Also, the one at the back appears to be longer for both 2.4 and 5.8?
Finally, what should the distances be between them?
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